Immunological control of microbial pathogens through vaccination is an effective way of dealing with many infectious diseases. Live avirulent Salmonella have been shown to be safe, effective delivery vehicles for a wide variety of recombinant antigens and induce systemic and mucosal immunity. The Principal Investigator has shown the feasibility of using Salmonella to effectively deliver a putative virulence factor HagB from Porphyromonas gingivalis resulting in systemic and mucosal immune responses. Many questions remain concerning the basic immunology of live oral vectors. Factors such as recombinant gene expression level and cellular localization can affect the characteristics of the immune response. The ability to control the characteristics of the immune response, the immunogenicity of the foreign antigen and the induction of memory are all desirable goals for the design of any vaccine. To address these questions three Specific Aims are proposed. Aim 1 will construct strains of S. typhimurium expressing variable levels of HagB, characterize the effects of expression level on vaccine viability and immunogenicity, evaluate the immune response parameters including the magnitude, duration and antibody isotype distribution in serum, saliva and vaginal washes, and examine the effects on IgG subclass distribution. Aim 2 proposes to construct strains of S. typhimurium which express HagB on their surface, to assess the effects of surface expression on membrane integrity, viability, growth rate, and immunogenicity, to evaluate the effects of surface expression on the magnitude, duration and antibody isotype distribution in serum, saliva and vaginal washes and to examine the effects on IgG subclass distribution. Aim 3 will compare differences in priming, boosting and long-term memory induction by strains expressing varying levels of HagB cytoplasmically, or surface localized HagB. In selected experiments, the immune responses and memory induction will be compared using another P. gingivalis potential virulence factor, HagA. These studies will aid in the current understanding of the effects of vaccine parameters on immunogenicity, the pattern of the immune response and factors which affect induction of long-term memory and recall.